Investments - Schedule of Lease Intangible Assets and Liabilities, Net of Accumulated Amortization (Details) - USD ($) $ in Thousands |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Capital Leased Assets [Line Items] | ||
| Less: accumulated amortization | $ (242,117) | $ (271,288) |
| Intangible lease assets, net | 396,596 | 409,903 |
| Less: accumulated amortization | (55,084) | (61,339) |
| Intangible lease liabilities, net | 151,179 | 155,303 |
| In-place leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease assets, gross | 554,197 | 591,551 |
| Above-market leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease assets, gross | 84,516 | 89,640 |
| Below-market leases | ||
| Capital Leased Assets [Line Items] | ||
| Intangible lease liabilities, gross | $ 206,263 | $ 216,642 |